Flow Velocity Sensor Based on Double Fiber Bragg Gratings

By using the fiber grating pressure sensing setup and Venturi tube,a novel flow velocity sensor based on double fiber Bragg gratings(FBGs) is proposed. The relationship between the flow velocity and the wavelength shift difference is derived. The pressure difference of the two sides of the cross section of the aluminum foil tube in the pressure sensing setup results in the distortion of an isosceles triangle cantilever structure. And the distortion results in the Bragg wavelength shift of the FBGs mounted at either side of the cantilever. By monitoring the wavelength shift difference of the two FBGs,the flow velocity can be obtained. The cross sensitive problem can be solved by compensating the temperature effect. Experimental results are in good agreement with theoretical analysis. The central wavelength of two FBGs shifts to the shorter and longer wavelength respectively with the rise of the flow velocity,while the bandwidth is almost unchanged. The experimental results verify the feasibility of the proposed sensor with a measurement range of 8～200mm/s.